山东昌乐刚玉巨晶中的流体和熔融包裹体及其流体组分特征

Fluid and melt inclusions and their fluid species in corundum megacrysts from th e basalts in Changle,Shandong Province,eastern China

山东昌乐第三纪玄武岩中产有刚玉巨晶,内含丰富的原生和假次生流体包裹体和熔融包裹体。流体包裹体可分为CO2单相包裹体、H2O-CO2两相和三相包裹体。熔融包裹体类型复杂,其中富流体相包裹体可分为含CO2收缩气泡两相熔融包裹体和气-液-固多相熔融包裹体。诸类包裹体主要赋含在刚玉晶核外的“主体”部分,以CO2单相流体包裹体和两相熔融包裹体最为发育,并且不同类型包裹体常密切伴生,表明它们形成时流体发生了不混溶作用:出现熔浆相(富含挥发分)、气相(CO2为主)和富水相(H2O-CO2为主)等多相体系。激光拉曼分析结果显示,各类包裹体中的气体组分主要是CO2,另有不等量的N2和H2S,据此划分为纯CO2、CO2-N2、CO2-H2S和CO2-N2-H2S等气体组合类型,没有发现O2、CH4和H2等组分。此外,拉曼分析也证实了流体包裹体和熔融包裹体中存在H2O。上述资料表明,昌乐地区深部流体以CO2为主,同时包含H2O、N2和H2S在内的多种组分,这些流体组分也是刚玉母浆系统的重要成分。

Corundum megacrysts occur in the Cenozoic basalts from Changle, Shandong Province, eastern China. There are a lot of primary and pseudo-secondary fluid and melt inclusions in the megacrysts. Three types of fluid inclusions have been identified： CO2 single-phase fluid inclusion, H2O-CO2 two-phase fluid inclusion and H2O-CO2 three-phase inclusion. The melt inclusions are quite complicated, in which the fluids-rich are classified into two groups： CO2 shrinkage bubble-rich two-phase melt inclusion and multi-phase melt inclusion containing CO2 shrinkage bubbles, aqueous solution and daughter minerals. The fluid and melt inclusions above mainly occur in the main parts outside of the crystal core of the corundum megacryst. Comparatively, CO2 single-phase fluid inclusions and two-phase melt inclusions are more plentiful in amount among them. The different types of inclusions often coexist with each other, indicating that immiscible process took place in primary fluid-meh system. The process resulted in the separation of melt, gases （dominated by CO2） and H2O-rich phase （dominated by H2O and CO2）. Meanwhile, the gases species of CO2, N2 and H2S in inclusions are confirmed by Laser Raman analysis. Their contents in inclusions are variable, so different gases assemblages can be distinguished： pure CO2, CO2-N2 mixtures, CO2-H2S mixtures and CO2-N2-H2S mixtures. CO2 is dominant for whatever gases assemblages. In addition, the presence of H2O is also confirmed by Raman analysis. Fluid species in fluid and melt inclusions indicate that deeply derived fluid system in the Changle area is dominated by CO2, with minor H2O, N2 and H2S etc. It also suggests that corundum megacrysts were crystallized in fluid-melt environment.